GitLab

* Moved git information to left prompt, with
  support for:
    * +ZSH_THEME_GIT_PROMPT_UNTRACKED, MODIFIED,
    STASHED, ADDED, UPSTREAM STATUS
    (if applicable)
* Removed right prompt
* Refactored following Google's guidelines for
  scripts [ http://goo.gl/oJSXH2 ]
    * Using local variables where applicable